Semiconductor device and method

ABSTRACT

An embodiment is a semiconductor device including a first channel region over a semiconductor substrate, a second channel region over the first channel region, a first gate stack over the semiconductor substrate and surrounding the first channel region and the second channel region, a first inner spacer extending from the first channel region to the second channel region and along a sidewall of the first gate stack, a second inner spacer extending from the first channel region to the second channel region and along a sidewall of the first inner spacer, the second inner spacer having a different material composition than the first inner spacer, and a first source/drain region adjacent the first channel region, the second channel region, and the second inner spacer, the first and second inner spacers being between the first gate stack and the first source/drain region.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.62/953,824, filed on Dec. 26, 2019, which application is herebyincorporated herein by reference.

BACKGROUND

Semiconductor devices are used in a variety of electronic applications,such as, for example, personal computers, cell phones, digital cameras,and other electronic equipment. Semiconductor devices are typicallyfabricated by sequentially depositing insulating or dielectric layers,conductive layers, and semiconductor layers of material over asemiconductor substrate, and patterning the various material layersusing lithography to form circuit components and elements thereon.

The semiconductor industry continues to improve the integration densityof various electronic components (e.g., transistors, diodes, resistors,capacitors, etc.) by continual reductions in minimum feature size, whichallow more components to be integrated into a given area. However, asthe minimum features sizes are reduced, additional problems arise thatshould be addressed.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 illustrates an example of a semiconductor device includingnanostructure field-effect transistors (NSFETs) in a three-dimensionalview, in accordance with some embodiments.

FIGS. 2, 3, 4, 5, 6A, 6B, 7A, 7B, 8A, 8B, 8C, 9A, 9B, 10A, 10B, 10C,11A, 11B, 12A, 12B, 13A, 13B, 14A, 14B, 15A, 15B, 15C, 16A, 16B, 17A,17B, 18A, 18B, 19A, 19B, 20A, 20B, 21A, 21B, 22A, and 22B arecross-sectional views of intermediate stages in the manufacturing ofsemiconductor devices, in accordance with some embodiments.

FIGS. 23, 24, 25A, 25B, 26A, and 26B are cross-sectional views ofintermediate stages in the manufacturing of semiconductor devices, inaccordance with some embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the invention. Specificexamples of components and arrangements are described below to simplifythe present disclosure. These are, of course, merely examples and arenot intended to be limiting. For example, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed between the first and second features, such thatthe first and second features may not be in direct contact. In addition,the present disclosure may repeat reference numerals and/or letters inthe various examples. This repetition is for the purpose of simplicityand clarity and does not in itself dictate a relationship between thevarious embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

Various embodiments provide semiconductor devices and methods of formingthe same in which nanostructures are designed to control the shapes anddimensions of the replacement gate and inner spacer structures. Inspecific embodiments, the atomic concentration of an element (e.g., Ge)in a semiconductor compound of a sacrificial layer may controlled andvaried to control the shape and dimensions of the replacement gatestructure. Further, the atomic concentration of an element (e.g., Ge) ina semiconductor compound of a sacrificial layer may controlled andvaried to control the length of the channel region of the nanostructuredevice. By controlling the shape and dimensions of the replacement gatestructure and channel length, the electrical properties of thenanostructure device can be improved, and the uniformity of thenanostructure device can be improved. In further embodiments, the innerspacer structure may include multiple spacer layers which can improvethe etching resistance of the inner spacer structure while also loweringthe capacitance for the nanostructure device.

FIG. 1 illustrates an example of nanostructure (e.g., nanosheet,nanowire, gate-all-around, or the like) field effect transistors(NSFETs), in accordance with some embodiments. The NSFETs comprisenanostructures 55 over a substrate 50 (e.g., a semiconductor substrate).The nanostructures 55 include second semiconductor layers 54A-54C, whichact as channel regions of the nanostructures 55. Shallow trenchisolation (STI) regions 58 are disposed in the substrate 50, and thenanostructures 55 are disposed above and between neighboring STI regions58. Although the STI regions 58 are described/illustrated as beingseparate from the substrate 50, as used herein, the term “substrate” mayrefer to the semiconductor substrate alone or a combination of thesemiconductor substrate and the STI regions.

Gate dielectric layers 100 are along top surfaces, sidewalls, and bottomsurfaces of the nanostructures 55, such as on top surfaces, sidewalls,and bottom surfaces of each of the second semiconductor layers 54A-54C,and along top surfaces and sidewalls of portions of the substrate 50.Gate electrodes 102 are over the gate dielectric layers 100. Epitaxialsource/drain regions 92 are disposed on opposite sides of thenanostructures 55, the gate dielectric layers 100, and the gateelectrodes 102. FIG. 1 further illustrates reference cross-sections thatare used in later figures. Cross-section A-A′ is along a longitudinalaxis of a gate electrode 102 and in a direction, for example,perpendicular to the direction of current flow between the epitaxialsource/drain regions 92 of the NSFETs. Cross-section B-B′ isperpendicular to cross-section A-A′ and is along a longitudinal axis ofa nanostructure 55 and in a direction of, for example, the current flowbetween the epitaxial source/drain regions 92 of the NSFETs.Cross-section C-C′ is parallel to cross-section A-A′ and extends throughthe epitaxial source/drain regions 92 of the NSFETs. Subsequent figuresrefer to these reference cross-sections for clarity.

Some embodiments discussed herein are discussed in the context of NSFETsformed using gate-last processes. In other embodiments, a gate-firstprocess may be used. Also, some embodiments contemplate aspects used infin field effect transistors (FinFETs) or planar devices, such as planarFETs.

FIGS. 2 through 22B are cross-sectional views of intermediate stages inthe manufacturing of NSFETs, in accordance with some embodiments. FIGS.2 through 5, 6A, 16A, 17A, 18A, 19A, 20A, 21A, and 22A illustratereference cross-section A-A′ illustrated in FIG. 1 . FIGS. 6B, 7B, 8B,8C, 9B, 10B, 11A, 12A, 13A, 14B, 15B, 16B, 17B, 18B, 19B, 20B, 21B, and22B illustrate reference cross-section B-B′ illustrated in FIG. 1 .FIGS. 7A, 8A, 9A, 10A, 14A, 15A, and 15C illustrate referencecross-section C-C′ illustrated in FIG. 1 .

In FIG. 2 , a substrate 50 is provided for forming NSFETs. The substrate50 may be a semiconductor substrate, such as a bulk semiconductor, asemiconductor-on-insulator (SOI) substrate, or the like, which may bedoped (e.g., with a p-type or an n-type dopant) or undoped. Thesubstrate 50 may be a wafer, such as a silicon wafer. Generally, an SOIsubstrate is a layer of a semiconductor material formed on an insulatorlayer. The insulator layer may be, for example, a buried oxide (BOX)layer, a silicon oxide layer, or the like. The insulator layer isprovided on a substrate, typically a silicon or glass substrate. Othersubstrates, such as a multi-layered or gradient substrate may also beused. In some embodiments, the semiconductor material of the substrate50 may include silicon; germanium; a compound semiconductor includingsilicon carbide, gallium arsenide, gallium phosphide, indium phosphide,indium arsenide, and/or indium antimonide; an alloy semiconductorincluding silicon-germanium, gallium arsenide phosphide, aluminum indiumarsenide, aluminum gallium arsenide, gallium indium arsenide, galliumindium phosphide, and/or gallium indium arsenide phosphide; orcombinations thereof.

The substrate 50 has a region 50N and a region 50P. The region 50N canbe for forming n-type devices, such as NMOS transistors, e.g., n-typeNSFETs. The region 50P can be for forming p-type devices, such as PMOStransistors, e.g., p-type NSFETs. The region 50N may be physicallyseparated from the region 50P (as illustrated by divider 51), and anynumber of device features (e.g., other active devices, doped regions,isolation structures, etc.) may be disposed between the region 50N andthe region 50P.

The substrate 50 may be lightly doped with a p-type or an n-typeimpurity. An anti-punch-through (APT) implantation may be performed onan upper portion of the substrate 50 to form an APT region 53. Duringthe APT implantation, dopants may be implanted in the region 50N and theregion 50P. The dopants may have a conductivity type opposite aconductivity type of source/drain regions (such as the epitaxialsource/drain regions 92, discussed below with respect to FIGS. 15A-15C12A 12C) to be formed in each of the region 50N and the region 50P. TheAPT region 53 may extend under the subsequently formed source/drainregions in the resulting NSFETs, which will be formed in subsequentprocesses. The APT region 53 may be used to reduce the leakage from thesource/drain regions to the substrate 50. In some embodiments, thedoping concentration in APT region 53 may be from about 1×1018 atoms/cm3to about 1×1019 atoms/cm3, such as about 5.5×1018 atoms/cm3. Forsimplicity and legibility, the APT region 53 is not illustrated insubsequent drawings.

Further in FIG. 2 , a multi-layer stack 56 is formed over the substrate50. The multi-layer stack 56 includes alternating first semiconductorlayers 52 and second semiconductor layers 54 of different semiconductormaterials. The first semiconductor layers 52 may be formed of firstsemiconductor materials, which may include, for example, silicongermanium (SiGe) or the like. The second semiconductor layers 54 may beformed of second semiconductor materials, which may include, forexample, silicon (Si), silicon carbide (SiC), or the like. In otherembodiments, the first semiconductor layers 52 may be formed of thesecond semiconductor materials and the second semiconductor layers 54may be formed of the first semiconductor materials. For purposes ofillustration, the multi-layer stack 56 includes three of the firstsemiconductor layers 52 (e.g., first semiconductor layers 52A-52C) andthree of the second semiconductor layers 54 (e.g., second semiconductorlayers 54A-54C). In other embodiments, the multi-layer stack 56 mayinclude any number of the first semiconductor layers 52 and the secondsemiconductor layers 54. Each of the layers of the multi-layer stack 56may be epitaxially grown using a process such as chemical vapordeposition (CVD), atomic layer deposition (ALD), vapor phase epitaxy(VPE), molecular beam epitaxy (MBE), or the like.

In some embodiments, the first semiconductor layers 52 have variedcompositions. For example, the atomic concentration of germanium in thefirst semiconductor layers 52 can be varied. As an example, the flowrates of the precursors used to epitaxially grow the first semiconductorlayers 52 can be varied to achieve the first semiconductor layers 52with different compositions. By varying the atomic concentration ofgermanium in the first semiconductor layers 52, the etching rate of thefirst semiconductor layers 52 can be different to allow each of thefirst semiconductor layers to have the same length between subsequentlyformed source/drain regions. In some embodiments, the atomicconcentration of germanium can decrease moving from the bottom firstsemiconductor layer 52A to the top first semiconductor layer 52C. Forexample, the atomic concentration of germanium in the bottom firstsemiconductor layer 52A can range from about 30% to about 40%, such asabout 35%, the atomic concentration of germanium in the middle firstsemiconductor layer 52B can range from about 25% to about 35%, such asabout 30%, and the atomic concentration of germanium in the top firstsemiconductor layer 52C can range from about 20% to about 30%, such asabout 25%. By increasing the amount of germanium in the lower layers ofthe first semiconductor layers 52, the etch rate for those lower layerscan be greater than the upper layers of the first semiconductor layers52 such that the lower layers 52 can etch the same amount as the upperlayers 52 even though the upper layers 52 are exposed to the etchprocess for a longer time. In some embodiments, each of the firstsemiconductor layers 52 has a different atomic concentration ofgermanium relative to the other first semiconductor layers 52 but has asame atomic concentration throughout the entirety of that firstsemiconductor layer.

For purposes of illustration, the second semiconductor layers 54 will bedescribed as forming channel regions in completed NSFET devices. Thefirst semiconductor layers 52 may be sacrificial layers, which may besubsequently removed. Nevertheless, in some embodiments the secondsemiconductor layers 54A-54C may form channel regions in completed NSFETdevices, while the first semiconductor layers 52A-52D may be sacrificiallayers.

In FIG. 3 , nanostructures 55 are formed in the multi-layer stack 56 andthe substrate 50 is etched. In some embodiments, the nanostructures 55(sometimes referred to as multi-layer fin structures 55) may be formedby etching trenches in the multi-layer stack 56 and the substrate 50.The etching may be any acceptable etch process, such as a reactive ionetch (RIE), neutral beam etch (NBE), the like, or a combination thereof.The etching may be anisotropic.

The nanostructures 55 and the substrate 50 may be patterned by anysuitable method. For example, the nanostructures 55 and the substrate 50may be patterned using one or more photolithography processes, includingdouble-patterning or multi-patterning processes. Generally,double-patterning or multi-patterning processes combine photolithographyand self-aligned processes, allowing patterns to be created that have,for example, pitches smaller than what is otherwise obtainable using asingle, direct photolithography process. For example, in one embodiment,a sacrificial layer is formed over a substrate and patterned using aphotolithography process. Spacers are formed alongside the patternedsacrificial layer using a self-aligned process. The sacrificial layer isthen removed, and the remaining spacers may then be used to pattern thenanostructures 55 and the substrate 50. In some embodiments, a mask (orother layer) may remain on the nanostructures 55 after patterning thenanostructures 55 and the substrate 50.

In FIG. 4 , shallow trench isolation (STI) regions 58 are formedadjacent the nanostructures 55 and the patterned portions of thesubstrate 50. The STI regions 58 may be formed by forming an insulationmaterial (not separately illustrated) over the substrate 50 and betweenneighboring nanostructures 55/patterned portions of the substrate 50.The insulation material may be an oxide, such as silicon oxide, anitride, the like, or a combination thereof, and may be formed by a highdensity plasma chemical vapor deposition (HDP-CVD), a flowable CVD(FCVD) (e.g., a CVD-based material deposition in a remote plasma systemwith post curing to convert the deposited material to another material,such as an oxide), the like, or a combination thereof. Other insulationmaterials formed by any acceptable process may be used. In theillustrated embodiment, the insulation material is silicon oxide formedby an FCVD process. An anneal process may be performed once theinsulation material is formed. In an embodiment, the insulation materialis formed such that excess insulation material covers the nanostructures55. The insulation material may comprise a single layer or may utilizemultiple layers. For example, in some embodiments a liner (notseparately illustrated) may first be formed along surfaces of thesubstrate 50 and the nanostructures 55. Thereafter, a fill material,such as those discussed above may be formed over the liner.

A removal process is then applied to the insulation material to removeexcess insulation material over the nanostructures 55. In someembodiments, a planarization process such as a chemical mechanicalpolish (CMP), an etch-back process, combinations thereof, or the likemay be utilized. The planarization process may planarize the insulationmaterial and the nanostructures 55. The planarization process exposesthe nanostructures 55 such that top surfaces of the nanostructures 55and the insulation material are level after the planarization process iscomplete.

The insulation material is then recessed to form the STI regions 58 asillustrated in FIG. 4 . The insulation material is recessed such thatupper portions of the nanostructures 55 and the substrate 50 protrudefrom between neighboring STI regions 58. Further, the top surfaces ofthe STI regions 58 may have flat surfaces as illustrated, convexsurfaces, concave surfaces (such as dishing), or a combination thereof.The top surfaces of the STI regions 58 may be formed flat, convex,and/or concave by an appropriate etch. The STI regions 58 may berecessed using an acceptable etching process, such as one that isselective to the material of the insulation material (e.g., etches thematerial of the insulation material at a faster rate than the materialof the nanostructures 55 and the substrate 50). For example, an oxideremoval using, for example, dilute hydrofluoric (dHF) acid may be used.

The process described with respect to FIGS. 2-4 is just one example ofhow the nanostructures 55 may be formed. In some embodiments, thenanostructures 55 may be formed by epitaxial growth processes. Forexample, dielectric layers may be formed over top surfaces of thesubstrate 50, and trenches may be etched through the dielectric layersto expose the underlying substrate 50. Epitaxial structures may beepitaxially grown in the trenches, and the dielectric layers may berecessed such that the epitaxial structures protrude from the dielectriclayer to form the nanostructures 55. In the nanostructures 55, theepitaxial structures may comprise alternating layers of the firstsemiconductor materials and the second semiconductor materials. Thesubstrate 50 may include epitaxial structures, which may behomoepitaxial structures or heteroepitaxial structures. The dielectriclayers may be subsequently recessed such that the nanostructures 55 andportions of the substrate 50 protrude from the dielectric layer. Inembodiments where the nanostructures 55 and portions of the substrate 50are epitaxially grown, the epitaxially grown materials may be in situdoped during growth, which may obviate prior and subsequentimplantations, although in situ and implantation doping may be usedtogether.

Still further, it may be advantageous to epitaxially grow material inthe region 50N (e.g., the NMOS region) different from the materials inthe region 50P (e.g., the PMOS region). In various embodiments, upperportions of the substrate 50 may be formed from silicon-germanium(Si_(x)Ge_(1-x), where x can be in the range of 0 to 1), siliconcarbide, pure or substantially pure germanium, a III-V compoundsemiconductor, a II-VI compound semiconductor, or the like. For example,the available materials for forming III-V compound semiconductorinclude, but are not limited to, indium arsenide, aluminum arsenide,gallium arsenide, indium phosphide, gallium nitride, indium galliumarsenide, indium aluminum arsenide, gallium antimonide, aluminumantimonide, aluminum phosphide, gallium phosphide, and the like.

Further in FIG. 4 , appropriate wells (not separately illustrated) maybe formed in the nanostructures 55 and/or the substrate 50. In someembodiments, P wells may be formed in the region 50N, and N wells may beformed in the region 50P. In further embodiments, P wells or N wells maybe formed in each of the region 50N and the region 50P.

In embodiments including different well types, different implant stepsfor the region 50N and the region 50P may be achieved using aphotoresist or other masks (not separately illustrated). For example, aphotoresist may be formed over the nanostructures 55, the substrate 50,and the STI regions 58 in the region 50N. The photoresist is patternedto expose the region 50P of the substrate 50. The photoresist can beformed by using a spin-on technique and can be patterned usingacceptable photolithography techniques. Once the photoresist ispatterned, an n-type impurity implant is performed in the region 50P,and the photoresist may act as a mask to substantially prevent n-typeimpurities from being implanted into the region 50N. The n-typeimpurities may be phosphorus, arsenic, antimony, or the like implantedin the region to a concentration of equal to or less than 1×10¹⁸atoms/cm³, such as from about 1×10¹⁶ atoms/cm³ to about 1×10¹⁸atoms/cm³, or about 5.05×10¹⁷ atoms/cm³. After the implant, thephotoresist is removed, such as by an acceptable ashing process.

Following the implanting of the region 50P, a photoresist is formed overthe nanostructures 55, the substrate 50, and the STI regions 58 in theregion 50P. The photoresist is patterned to expose the region 50N of thesubstrate 50. The photoresist can be formed by using a spin-on techniqueand can be patterned using acceptable photolithography techniques. Oncethe photoresist is patterned, a p-type impurity implant may be performedin the region 50N, and the photoresist may act as a mask tosubstantially prevent p-type impurities from being implanted into theregion 50P. The p-type impurities may be boron, boron fluoride, indium,or the like implanted in the region to a concentration of equal to orless than 1×10¹⁸ atoms/cm³, such as from about 1×10¹⁶ atoms/cm³ to about1×10¹⁸ atoms/cm³, or about 5.05×10¹⁷ atoms/cm³. After the implant, thephotoresist may be removed, such as by an acceptable ashing process.

After the implants of the region 50N and the region 50P, an anneal maybe performed to repair implant damage and to activate the p-type and/orn-type impurities that were implanted. In some embodiments, the grownmaterials of epitaxial fins may be in situ doped during growth, whichmay obviate the implantations, although in situ and implantation dopingmay be used together.

In FIG. 5 , dummy dielectric layers 60 are formed on the nanostructures55 and the substrate 50. The dummy dielectric layers 60 may be, forexample, silicon oxide (SiO), silicon nitride (SiN), a combinationthereof, or the like, and may be deposited or thermally grown accordingto acceptable techniques. A dummy gate layer 62 is formed over the dummydielectric layers 60, and a mask layer 64 is formed over the dummy gatelayer 62. The dummy gate layer 62 may be deposited over the dummydielectric layers 60 and then planarized by a process such as CMP. Themask layer 64 may be deposited over the dummy gate layer 62. The dummygate layer 62 may be conductive or non-conductive materials and may beselected from a group including amorphous silicon,polycrystalline-silicon (polysilicon), polycrystalline silicon-germanium(poly-SiGe), metallic nitrides, metallic silicides, metallic oxides, andmetals. The dummy gate layer 62 may be deposited by physical vapordeposition (PVD), CVD, sputter deposition, or other techniques known andused in the art for depositing the selected material. The dummy gatelayer 62 may be made of other materials that have a high etchingselectivity from the material of the STI regions 58. The mask layer 64may include, for example, silicon nitride, silicon oxynitride, or thelike. In this example, a single dummy gate layer 62 and a single masklayer 64 are formed across the region 50N and the region 50P. It isnoted that the dummy dielectric layers 60 are shown covering only thenanostructures 55 and the substrate 50 for illustrative purposes only.In some embodiments, the dummy dielectric layers 60 may be depositedsuch that the dummy dielectric layers 60 cover the STI regions 58,extending between the dummy gate layer 62 and the STI regions 58.

FIGS. 6A through 19B illustrate various additional steps in themanufacturing of embodiment devices. FIGS. 6B through 19B illustratefeatures in either of the region 50N or the region 50P. For example, thestructures illustrated in FIGS. 6B through 19B may be applicable to boththe region 50N and the region 50P. Differences (if any) in thestructures of the region 50N and the region 50P are described in thetext accompanying each figure.

In FIGS. 6A and 6B, the mask layer 64 (see FIG. 5 ) may be patternedusing acceptable photolithography and etching techniques to form masks74. An acceptable etching technique may be used to transfer the patternof the masks 74 to the dummy gate layer 62 to form dummy gates 72. Insome embodiments, the pattern of the masks 74 may also be transferred tothe dummy dielectric layers 60. The dummy gates 72 cover respectivechannel regions of the nanostructures 55. In an embodiment, the channelregions may be formed in the second semiconductor layers 54A-54Cincluding the second semiconductor materials. The pattern of the masks74 may be used to physically separate each of the dummy gates 72 fromadjacent dummy gates 72. The dummy gates 72 may have a lengthwisedirection substantially perpendicular to lengthwise directions ofrespective nanostructures 55.

In FIGS. 7A and 7B, a first spacer layer 80 and a second spacer layer 82are formed over the structures illustrated in FIGS. 6A and 6B. In FIGS.7A and 7B, the first spacer layer 80 is formed on top surfaces of theSTI regions 58, top surfaces and sidewalls of the nanostructures 55 andthe masks 74, and sidewalls of the substrate 50, the dummy gates 72 andthe dummy dielectric layers 60. The second spacer layer 82 is depositedover the first spacer layer 80. The first spacer layer 80 may be formedby thermal oxidation or deposited by CVD, ALD, or the like. The firstspacer layer 80 may be formed of silicon oxide, silicon nitride, siliconoxynitride, or the like. The second spacer layer 82 may be deposited byCVD, ALD, or the like. The second spacer layer 82 may be formed ofsilicon oxide, silicon nitride, silicon oxynitride, or the like.

In FIGS. 8A and 8B, the first spacer layer 80 and the second spacerlayer 82 are etched to form first spacers 81 and second spacers 83. Thefirst spacer layer 80 and the second spacer layer 82 may be etched usinga suitable etching process, such as an isotropic etching process (e.g.,a wet etching process), an anisotropic etching process (e.g., a dryetching process), or the like. As illustrated in FIG. 8A, the firstspacers 81 and the second spacers 83 are disposed on sidewalls of thenanostructures 55 and the substrate 50. As illustrated in FIG. 8B, thesecond spacer layer 82 may be removed from over the first spacer layer80 adjacent the masks 74, the dummy gates 72, and the dummy dielectriclayers 60 and the first spacers 81 are disposed on sidewalls of themasks 74, the dummy gates 72, and the dummy dielectric layers 60. Inanother embodiment, as illustrated in FIG. 8C, some portion of thesecond spacer layer 82 remains on the first spacer layer 80 adjacent themasks 74, the dummy gates 72, and the dummy dielectric layers 60 and thesecond spacers 83 are disposed on sidewalls of the masks 74, the dummygates 72, and the dummy dielectric layers 60.

After the first spacers 81 and the second spacers 83 are formed,implants for lightly doped source/drain (LDD) regions (not separatelyillustrated) may be performed. In embodiments with different devicetypes, similar to the implants discussed above in FIG. 4 , a mask, suchas a photoresist, may be formed over the region 50N, while exposing theregion 50P, and appropriate type (e.g., p-type) impurities may beimplanted into the exposed nanostructures 55 and the substrate 50 in theregion 50P. The mask may then be removed. Subsequently, a mask, such asa photoresist, may be formed over the region 50P while exposing theregion 50N, and appropriate type impurities (e.g., n-type) may beimplanted into the exposed nanostructures 55 and the substrate 50 in theregion 50N. The mask may then be removed. The n-type impurities may bethe any of the n-type impurities previously discussed, and the p-typeimpurities may be the any of the p-type impurities previously discussed.The lightly doped source/drain regions may have a concentration ofimpurities of from about 1×10¹⁵ atoms/cm³ to about 1×10¹⁹ atoms/cm³,such as about 5×10¹⁸ atoms/cm³. An anneal may be used to repair implantdamage and to activate the implanted impurities.

It is noted that the above disclosure generally describes a process offorming spacers and LDD regions. Other processes and sequences may beused. For example, fewer or additional spacers may be utilized,different sequence of steps may be utilized (e.g., the first spacers 81may be formed prior to forming the second spacers 83, additional spacersmay be formed and removed, and/or the like. Furthermore, the n-type andp-type devices may be formed using a different structures and steps.

In FIGS. 9A and 9B, first recesses 86 are formed in the nanostructures55 and the substrate 50. The first recesses 86 may extend through thefirst semiconductor layers 52A-52C and the second semiconductor layers54A-54C, and into the substrate 50. As illustrated in FIG. 9A, topsurfaces of the STI regions 58 may be level with a top surface of thesubstrate 50. In various embodiments, the first recesses may extend to atop surface of the substrate 50 without etching the substrate 50; thesubstrate 50 may be etched such that bottom surfaces of the firstrecesses 86 are disposed below the top surfaces of the STI regions 58;or the like. The first recesses 86 may be formed by etching thenanostructures 55 and the substrate 50 using anisotropic etchingprocesses, such as RIE, NBE, or the like. In some embodiments,anisotropic etching processes include etchants such as hydrogen bromide(HBr), chlorine (Cl₂), the like, or a combination thereof. The firstspacers 81, the second spacers 83, and the masks 74 mask portions of thenanostructures 55 and the substrate 50 during the etching processes usedto form the first recesses 86. A single etch process may be used to etcheach layer of the multi-layer stack 56. In other embodiments, multipleetch processes may be used to etch the layers of the multi-layer stack56. Timed etch processes may be used to stop the etching of the firstrecesses 86 after the first recesses 86 reach a desired depth.

In FIGS. 10A and 10B, portions of sidewalls of the layers of themulti-layer stack 56 formed of the first semiconductor materials (e.g.,the first semiconductor layers 52A-52C) exposed by the first recesses 86are etched to form sidewall recesses 88. FIG. 10C illustrates a detailedview of a portion of a multi-layer stack 56 from FIG. 10B. The sidewallsmay be etched using isotropic etching processes, such as wet etching orthe like. In some embodiments, the recessed sidewalls of the firstsemiconductor layers 52A-52C have concave surfaces from the isotropicetching processes. The etchants used to etch the first semiconductorlayers 52A-52C may be selective to the first semiconductor materialssuch that the second semiconductor layers 54A-54C and the substrate 50remain relatively unetched as compared to the first semiconductor layers52A-52C. In an embodiment in which the first semiconductor layers52A-52C include, e.g., SiGe, and the second semiconductor layers 54A-54Cinclude, e.g., Si or SiC, ammonia (NH₃), tetramethylammonium hydroxide(TMAH), ammonium hydroxide (NH₄OH), or the like may be used to etchsidewalls of the multi-layer stack 56. In further embodiments, thelayers of the multi-layer stack 56 may be etched using a dry etchingprocess. Hydrogen fluoride, another fluorine-based gas, or the like maybe used to etch sidewalls of the multi-layer stack 56.

As illustrated in FIG. 10C, each of the first semiconductor layers 52A,52B, and 52C have a corresponding width W52A, W52B, and W52C measuredfrom opposing sidewalls of the first semiconductor layers 52A, 52B, and52C. In an embodiment in which the first semiconductor layers 52A-52Cinclude, e.g., SiGe, and where the atomic concentration of germaniumdecreases moving from the bottom first semiconductor layer 52A to thetop first semiconductor layer 52C, the widths W52A, W52B, and W52C aresubstantially equal after the isotropic etching process. By increasingthe amount of germanium in the lower layers of the first semiconductorlayers 52, the etch rate for those lower layers is greater than theupper layers of the first semiconductor layers 52 such that the lowerlayers 52 can etch the same amount as the upper layers 52, and thus,leading to substantially equal widths W52A, W52B, and W52C.

As illustrated in FIGS. 10B and 10C, isotropic etching processesgenerally form concave surfaces on the surfaces that they etch, such asthe concave surfaces of the sidewalls of the first semiconductor layers52A-52C in FIGS. 10B and 10C. In some embodiments, the firstsemiconductor layers 52A-52C can be modified to achieve different shapesfor the sidewall surfaces of the first semiconductor layers 52A-52C.FIGS. 11A-13B are cross-sectional views of intermediate stages similarto those of FIGS. 10A-10C in accordance with some of those otherembodiments. In FIGS. 11A-13B, the composition of the firstsemiconductor layers 52A-52C is modified to control the shape of thesidewall surfaces after they are recessed by an isotropic etchingprocess.

For the embodiments of FIGS. 11A-13B, the processing steps before theintermediate stage of processing in FIGS. 11A-13B can be achievedsimilar to that described in FIGS. 1-9B above and the description ofarriving at this intermediate stage of processing is not repeatedherein. Details regarding this embodiment that are similar to those forthe previously described embodiment will not be repeated herein.

In FIGS. 11A and 11B, the composition within each of the firstsemiconductor layers 52A-52C varies to enable the sidewall surface tohave a substantially planar shape. For example, when the top firstsemiconductor layer 52A includes, e.g., SiGe, the atomic concentrationof germanium (Ge) can be varied within the top first semiconductor layer52A to control the shape of the sidewall surface after the isotropicetching process. For the embodiment illustrated in FIGS. 11A and 11B,the atomic concentration of germanium (Ge) is higher in the top andbottom portions of the layer 52A (e.g., portions near the layer 54A andsubstrate 50) than the middle portion of the layer 52A. The transitionfrom the high concentration portion to the low concentration portion canbe a gradual transition or can be an abrupt or step-type transitiondepending on the desired sidewall surface shape. By having higheramounts of germanium in the in the top and bottom portions of each ofthe first semiconductor layers 52 than the respective middle portions ofthose layers 52, the etch rate for the top and bottom portions isgreater than the middle portions of those layers to allow for theisotropic etch process to produce a substantially planar sidewallsurface instead of the concave sidewall surface. In this embodiment, thefirst semiconductor layers 52B and 52C have a similar compositionprofile as first semiconductor layer 52A and the description is notrepeated herein.

In FIGS. 12A and 12B, the composition within each of the firstsemiconductor layers 52A-52C varies to enable the sidewall surface tohave a substantially notched shape. For example, when the top firstsemiconductor layer 52A includes, e.g., SiGe, the atomic concentrationof germanium (Ge) can be varied within the top first semiconductor layer52A to control the shape of the sidewall surface after the isotropicetching process. For the embodiment illustrated in FIGS. 12A and 12B,the atomic concentration of germanium (Ge) is lower in the top andbottom portions of the layer 52A (e.g., portions near the layer 54A andsubstrate 50) than the middle portion of the layer 52A. The transitionfrom the low concentration portion to the high concentration portion canbe a gradual transition or can be an abrupt or step-type transitiondepending on the desired sidewall surface shape. By having lower amountsof germanium in the in the top and bottom portions of each of the firstsemiconductor layers 52 than the respective middle portions of thoselayers 52, the etch rate for the top and bottom portions is less thanthe middle portions of those layers to allow for the isotropic etchprocess to produce a substantially notched sidewall surface instead ofthe concave sidewall surface. In this embodiment, the firstsemiconductor layers 52B and 52C have a similar composition profile asfirst semiconductor layer 52A and the description is not repeatedherein.

In FIGS. 13A and 13B, the composition within each of the firstsemiconductor layers 52A-52C varies to enable the sidewall surface tohave a substantially tapered shape. For example, when the top firstsemiconductor layer 52A includes, e.g., SiGe, the atomic concentrationof germanium (Ge) can be varied within the top first semiconductor layer52A to control the shape of the sidewall surface after the isotropicetching process. For the embodiment illustrated in FIGS. 13A and 13B,the atomic concentration of germanium (Ge) is higher in the upperportion of the layer 52A (e.g., portion near the layer 54A) than thelower portion of the layer 52A (e.g., portion near the substrate 50).The transition from the high concentration portion to the lowconcentration portion can be a gradual transition or can be an abrupt orstep-type transition depending on the desired sidewall surface shape. Byhaving higher amounts of germanium in the in the upper portion of eachof the first semiconductor layers 52 than the respective lower portionof those layers 52, the etch rate for the top portion is greater thanthe lower portion of those layers to allow for the isotropic etchprocess to produce a substantially tapered sidewall surface instead ofthe concave sidewall surface. In this embodiment, the firstsemiconductor layers 52B and 52C have a similar composition profile asfirst semiconductor layer 52A and the description is not repeatedherein.

FIGS. 14A-22B are cross-sectional views of intermediate stages in thecontinued manufacturing of the NSFETs, in accordance with someembodiments. While the subsequent steps in FIGS. 14A-22B are shown onthe embodiment of the first semiconductor layers 52A-52C of FIGS. 11Aand 11B (e.g., the embodiment with substantially planar sidewallsurfaces), the subsequent steps in FIGS. 14A-22B are also applicable tothe embodiments in FIGS. 10A-10C, 12A-12B, and 13A-13B.

In FIGS. 14A and 14B, inner spacers 90 are formed in the sidewall recess88. The inner spacers 90 may be formed by depositing an inner spacerlayer (not separately illustrated) over the structures illustrated inFIGS. 11A and 11B. The inner spacer layer may be deposited by aconformal deposition process, such as CVD, ALD, or the like. The innerspacer layer may comprise a material such as silicon nitride (SiN) orsilicon oxynitride (SiON), although any suitable material, such aslow-dielectric constant (low-k) materials having a k-value less thanabout 3.5, may be utilized. The inner spacer layer may then be etched toform the inner spacers 90. The inner spacer layer may be etched by ananisotropic etching process, such as RIE, NBE, or the like. The innerspacers 90 may be used to prevent damage to subsequently formedsource/drain regions (such as the epitaxial source/drain regions 92,discussed below with respect to FIGS. 15A-15C) by subsequent etchingprocesses.

In FIGS. 15A-15C, epitaxial source/drain regions 92 are formed in thefirst recesses 86 to exert stress on the second semiconductor layers54A-54C of the nanostructures 55, thereby improving performance. Asillustrated in FIG. 15B, the epitaxial source/drain regions 92 areformed in the first recesses 86 such that each dummy gate 72 is disposedbetween respective neighboring pairs of the epitaxial source/drainregions 92. In some embodiments, the first spacers 81 are used toseparate the epitaxial source/drain regions 92 from the dummy gates 72by an appropriate lateral distance so that the epitaxial source/drainregions 92 do not short out subsequently formed gates of the resultingNSFETs. The inner spacers 90 may be used to separate the epitaxialsource/drain regions 92 from the first semiconductor layers 52A-52C byappropriate lateral distances to prevent shorts between the epitaxialsource/drain regions 92 and the subsequently formed gates of theresulting NSFETs.

The epitaxial source/drain regions 92 in the region 50N, e.g., the NMOSregion, may be formed by masking the region 50P, e.g., the PMOS region.Then, the epitaxial source/drain regions 92 are epitaxially grown in thefirst recesses 86. The epitaxial source/drain regions 92 may include anyacceptable material, such as appropriate for n-type NSFETs. For example,if the second semiconductor layers 54A-54C are silicon, the epitaxialsource/drain regions 92 may include materials exerting a tensile strainon the second semiconductor layers 54A-54C, such as silicon, phosphorousdoped silicon, carbon doped silicon, carbon and phosphorous dopedsilicon, the like or a combination thereof. The epitaxial source/drainregions 92 may have surfaces raised from respective surfaces of themulti-layer stack 56 and may have facets.

The epitaxial source/drain regions 92 in the region 50P, e.g., the PMOSregion, may be formed by masking the region 50N, e.g., the NMOS region.Then, the epitaxial source/drain regions 92 are epitaxially grown in thefirst recesses 86. The epitaxial source/drain regions 92 may include anyacceptable material, such as appropriate for p-type NSFETs. For example,if the second semiconductor layers 54A-54C are silicon, the epitaxialsource/drain regions 92 may comprise materials exerting a compressivestrain on the second semiconductor layers 54A-54C, such assilicon-germanium, boron doped silicon-germanium, germanium, germaniumtin, or the like. The epitaxial source/drain regions 92 may also havesurfaces raised from respective surfaces of the multi-layer stack 56 andmay have facets.

The epitaxial source/drain regions 92, the second semiconductor layers54A-54C, and/or the substrate 50 may be implanted with dopants to formsource/drain regions, similar to the process previously discussed forforming lightly-doped source/drain regions, followed by an anneal. Thesource/drain regions may have an impurity concentration of between about1×10¹⁹ atoms/cm³ and about 1×10²¹ atoms/cm³, such as about 5.05×10²⁰atoms/cm³. The n-type and/or p-type impurities for source/drain regionsmay be any of the impurities previously discussed. In some embodiments,the epitaxial source/drain regions 92 may be in situ doped duringgrowth.

As a result of the epitaxy processes used to form the epitaxialsource/drain regions 92 in the region 50N and the region 50P, uppersurfaces of the epitaxial source/drain regions have facets which expandlaterally outward beyond sidewalls of the nanostructures 55. In someembodiments, these facets cause adjacent epitaxial source/drain regions92 of a same NSFET to merge as illustrated by FIG. 15A. In otherembodiments, adjacent epitaxial source/drain regions 92 remain separatedafter the epitaxy process is completed as illustrated by FIG. 15C. Inthe embodiments illustrated in FIGS. 15A and 15C, the first spacers 81may be formed covering portions of the sidewalls of the nanostructures55 and the substrate 50 that extend above the STI regions 58 therebyblocking the epitaxial growth. In some other embodiments, the spaceretch used to form the first spacers 81 may be adjusted to remove thespacer material to allow the epitaxially grown region to extend to thesurface of the STI region 58.

In FIGS. 16A and 16B, a first interlayer dielectric (ILD) 96 isdeposited over the structure illustrated in FIGS. 6A and 15B (theprocesses of FIGS. 7A-15B do not alter the cross-section illustrated inFIGS. 6A), respectively. The first ILD 96 may be formed of a dielectricmaterial, and may be deposited by any suitable method, such as CVD,plasma-enhanced CVD (PECVD), or FCVD. Dielectric materials may includephospho-silicate glass (PSG), boro-silicate glass (BSG), boron-dopedphospho-silicate glass (BPSG), undoped silicate glass (USG), or thelike. Other insulation materials formed by any acceptable process may beused. In some embodiments, a contact etch stop layer (CESL) 94 isdisposed between the first ILD 96 and the epitaxial source/drain regions92, the masks 74, and the first spacers 81. The CESL 94 may comprise adielectric material, such as, silicon nitride, silicon oxide, siliconoxynitride, or the like, having a different etch rate than the materialof the overlying first ILD 96.

In FIGS. 17A and 17B, a planarization process, such as a CMP, may beperformed to level the top surface of the first ILD 96 with the topsurfaces of the dummy gates 72 or the masks 74. The planarizationprocess may also remove the masks 74 on the dummy gates 72, and portionsof the first spacers 81 along sidewalls of the masks 74. After theplanarization process, top surfaces of the dummy gates 72, the firstspacers 81, and the first ILD 96 are level. Accordingly, the topsurfaces of the dummy gates 72 are exposed through the first ILD 96. Insome embodiments, the masks 74 may remain, in which case theplanarization process levels the top surface of the first ILD 96 withtop surface of the masks 74 and the first spacers 81.

In FIGS. 18A and 18B, the dummy gates 72, and the masks 74 if present,are removed in an etching step(s), so that second recesses 98 areformed. Portions of the dummy dielectric layers 60 in the secondrecesses 98 may also be removed. In some embodiments, only the dummygates 72 are removed and the dummy dielectric layers 60 remain and areexposed by the second recesses 98. In some embodiments, the dummydielectric layers 60 are removed from second recesses 98 in a firstregion of a die (e.g., a core logic region) and remain in secondrecesses 98 in a second region of the die (e.g., an input/outputregion). In some embodiments, the dummy gates 72 are removed by ananisotropic dry etch process. For example, the etching process mayinclude a dry etch process using reaction gas(es) that selectively etchthe dummy gates 72 at a faster rate than the first ILD 96 or the firstspacers 81. Each second recess 98 exposes and/or overlies portions ofthe multi-layer stack 56, which act as channel regions in subsequentlycompleted NSFETs. Portions of the multi-layer stack 56 which act as thechannel regions are disposed between neighboring pairs of the epitaxialsource/drain regions 92. During the removal, the dummy dielectric layers60 may be used as etch stop layers when the dummy gates 72 are etched.The dummy dielectric layers 60 may then be optionally removed after theremoval of the dummy gates 72.

In FIGS. 19A and 19B, the first semiconductor layers 52A-52C are removedextending the second recesses 98. The first semiconductor layers 52A-52Cmay be removed by an isotropic etching process such as wet etching orthe like. The first semiconductor layers 52A-52C may be removed usingetchants which are selective to the materials of the first semiconductorlayers 52A-52C, while the second semiconductor layers 54A-54C, thesubstrate 50, the STI regions 58 remain relatively unetched as comparedto the first semiconductor layers 52A-52C. In an embodiment in which thefirst semiconductor layers 52A-52C include, e.g., SiGe, and the secondsemiconductor layers 54A-54C include, e.g., Si or SiC, ammonia (NH₃),tetramethylammonium hydroxide (TMAH), ammonium hydroxide (NH₄OH), or thelike may be used to remove the first semiconductor layers 52A-52C.

In FIGS. 20A and 20B, gate dielectric layers 100 and gate electrodes 102are formed for replacement gates. The gate dielectric layers 100 aredeposited conformally in the second recesses 98, such as on top surfacesand sidewalls of the substrate 50 and on top surfaces, sidewalls, andbottom surfaces of the second semiconductor layers 54A-54C. The gatedielectric layers 100 may also be deposited on top surfaces of the firstILD 96, the CESL 94, the first spacers 81, and the STI regions 58. Inaccordance with some embodiments, the gate dielectric layers 100comprise silicon oxide, silicon nitride, or multilayers thereof. In someembodiments, the gate dielectric layers 100 include a high-k dielectricmaterial, and in these embodiments, the gate dielectric layers 100 mayhave a k value greater than about 7.0, and may include a metal oxide ora silicate of hafnium, aluminum, zirconium, lanthanum, manganese,barium, titanium, lead, and combinations thereof. The formation methodsof the gate dielectric layers 100 may include molecular-beam deposition(MBD), ALD, PECVD, and the like.

The gate electrodes 102 are deposited over the gate dielectric layers100, respectively, and fill the remaining portions of the secondrecesses 98. The gate electrodes 102 may include a metal-containingmaterial such as titanium nitride, titanium oxide, tantalum nitride,tantalum carbide, cobalt, ruthenium, aluminum, tungsten, combinationsthereof, or multi-layers thereof. For example, although single layergate electrodes 102 are illustrated in FIGS. 20A and 20B, the gateelectrodes 102 may comprise any number of liner layers, any number ofwork function tuning layers, and a fill material. Any combination of thelayers which make up the gate electrodes 102 may be deposited in theareas between each of the second semiconductor layers 54A-54C andbetween the second semiconductor layer 54A and the substrate 50. Afterthe filling of the second recesses 98, a planarization process, such asa CMP, may be performed to remove the excess portions of the gatedielectric layers 100 and the material of the gate electrodes 102, whichexcess portions are over the top surface of the first ILD 96. Theremaining portions of material of the gate electrodes 102 and the gatedielectric layers 100 thus form replacement gates of the resultingNSFETs. The gate electrodes 102 and the gate dielectric layers 100 maybe collectively referred to as “gate stacks.”

The formation of the gate dielectric layers 100 in the region 50N andthe region 50P may occur simultaneously such that the gate dielectriclayers 100 in each region are formed from the same materials, and theformation of the gate electrodes 102 may occur simultaneously such thatthe gate electrodes 102 in each region are formed from the samematerials. In some embodiments, the gate dielectric layers 100 in eachregion may be formed by distinct processes, such that the gatedielectric layers 100 may be different materials, and/or the gateelectrodes 102 in each region may be formed by distinct processes, suchthat the gate electrodes 102 may be different materials. Various maskingsteps may be used to mask and expose appropriate regions when usingdistinct processes.

In FIGS. 21A and 21B, a second ILD 110 is deposited over the first ILD96. In some embodiments, the second ILD 110 is a flowable film formed byFCVD. In some embodiments, the second ILD 110 is formed of a dielectricmaterial such as PSG, BSG, BPSG, USG, or the like, and may be depositedby any suitable method, such as CVD, PECVD, or the like. In accordancewith some embodiments, before the formation of the second ILD 110, thegate stack (including the gate dielectric layers 100 and thecorresponding overlying gate electrodes 102) is recessed, so that arecess is formed directly over the gate stack and between opposingportions of first spacers 81. A gate mask 108 comprising one or morelayers of dielectric material, such as silicon nitride, siliconoxynitride, or the like, is filled in the recess, followed by aplanarization process to remove excess portions of the dielectricmaterial extending over the first ILD 96. Subsequently formed gatecontacts (such as the gate contacts 114, discussed below with respect toFIGS. 22A and 22B) penetrate through the gate mask 108 to contact thetop surface of the recessed gate electrodes 102.

In FIGS. 22A and 22B, source/drain contacts 112 and gate contacts 114are formed through the second ILD 110 and the first ILD 96. Openings forthe source/drain contacts 112 are formed through the first ILD 96 andthe second ILD 110, and openings for the gate contacts 114 are formedthrough the second ILD 110 and the gate mask 108. The openings may beformed using acceptable photolithography and etching techniques. Aliner, such as a diffusion barrier layer, an adhesion layer, or thelike, and a conductive material are formed in the openings. The linermay include titanium, titanium nitride, tantalum, tantalum nitride, orthe like. The conductive material may be copper, a copper alloy, silver,gold, tungsten, cobalt, aluminum, nickel, or the like. A planarizationprocess, such as a CMP, may be performed to remove excess material froma surface of the second ILD 110. The remaining liner and conductivematerial form the source/drain contacts 112 and the gate contacts 114 inthe openings. An anneal process may be performed to form a silicide atthe interface between the epitaxial source/drain regions 92 and thesource/drain contacts 112. The source/drain contacts 112 are physicallyand electrically coupled to the epitaxial source/drain regions 92, andthe gate contacts 114 are physically and electrically coupled to thegate electrodes 102. The source/drain contacts 112 and the gate contacts114 may be formed in different processes, or may be formed in the sameprocess. Although shown as being formed in the same cross-sections, itshould be appreciated that each of the source/drain contacts 112 and thegate contacts 114 may be formed in different cross-sections, which mayavoid shorting of the contacts.

FIGS. 23 through 26B are cross-sectional views of intermediate stepsduring the manufacturing of the NSFETs, in accordance with someembodiments. FIG. 26A illustrates reference cross-section A-A′illustrated in FIG. 1 . FIGS. 23, 24, 25A, and 26B illustrate referencecross-section B-B′ illustrated in FIG. 1 . The embodiment in FIGS. 23through 26B is similar to the embodiments illustrated in FIGS. 1 through22B except that this embodiment includes two inner spacer layers.Details regarding this embodiment that are similar to those for thepreviously described embodiment will not be repeated herein.

FIG. 23 illustrates an intermediate stage of processing similar to thatdescribed in FIGS. 10A-10C above and the description of forming thisintermediate stage of processing is not repeated herein.

In FIG. 23 , a first inner spacer layer 90A is formed over the structureillustrated in FIGS. 10A-10C. The first inner spacer layer 90A may bedeposited by a conformal deposition process, such as CVD, ALD, or thelike. The first inner spacer layer 90A may comprise a material such assilicon carbonitride (SiCN), silicon carbide (SiC), siliconcarboxynitride (SiCON), the like, or a combination thereof. In someembodiments, the first inner spacer layer 90A is formed to have athickness in a range from about 0.5 nm to about 2 nm, such as 1.5 nm.

In FIG. 24 , a second inner spacer layer 90B is formed over the firstinner spacer layer 90A illustrated in FIG. 23 . The second inner spacerlayer 90B may be deposited by a conformal deposition process, such asCVD, ALD, or the like. The second inner spacer layer 90B may comprise amaterial such as silicon nitride (SiN), silicon carboxynitride (SiCON),silicon, silicon oxide (SiO), the like, or a combination thereof. Insome embodiments, the second inner spacer layer 90B is formed to have athickness in a range from about 2 nm to about 6 nm, such as 4 nm.

In FIGS. 25A and 25B, the first and second inner spacer layers 90A and90B may then be etched to form the inner spacers 91, which include innerspacers 91A and 91B. The first and second inner spacer layers 90A and90B may be etched by an anisotropic etching process, such as RIE, NBE,or the like. The inner spacers 91 may be used to prevent damage tosubsequently formed source/drain regions (such as the epitaxialsource/drain regions 92, discussed below with respect to FIGS. 26A and26B) by subsequent etching processes. By including multiple spacerlayers in the inner spacer structure, the etching resistance of theinner spacer structure is improved while also lowering the capacitancefor the nanostructure device. For example, the material for the firstinner spacer layer 90A can be selected for its enhanced etchingresistance during the replacement gate process while the material forthe second spacer layer 90B can be selected for its low-k value to lowerthe capacitance of the nanostructure device.

As illustrated in FIG. 25A, some of the inner spacer 91A can remain onthe spacers 81 on the sidewalls of the dummy gates 72. This remaininginner spacer 91A can provide extra protection for the sidewalls ofreplacement gate stacks 100/102 during subsequent processing.

In FIGS. 26A and 26B, subsequent processing is performed on thestructure of FIGS. 25A and 25B in the formation of the NSFETs. Thissubsequent processing is similar to the processing in FIGS. 15A-22Bdescribed above and the description is not repeated herein.

Although the embodiment of FIGS. 23 through 26B was illustrated anddescribed separately, its features may be combined with any of theprevious embodiments in the disclosure. For example, the firstsemiconductor layers 52A-52C with substantially planar sidewall surfaces(see, e.g., FIGS. 14A and 14B) may include the two layer inner spacerstructure 91A/B.

Embodiments may achieve advantages. In the disclosed embodiments,nanostructures are designed to control the shapes and dimensions of thereplacement gate and inner spacer structures. In specific embodiments,the atomic concentration of an element (e.g., Ge) in a semiconductorcompound of a sacrificial layer may controlled and varied to control theshape and dimensions of the replacement gate structure. Further, theatomic concentration of an element (e.g., Ge) in a semiconductorcompound of a sacrificial layer may controlled and varied to control thelength of the channel region of the nanostructure device. By controllingthe shape and dimensions of the replacement gate structure and channellength, the electrical properties of the nanostructure device can beimproved, and the uniformity of the nanostructure device can beimproved. In further embodiments, the inner spacer structure may includemultiple spacer layers which can improve the etching resistance of theinner spacer structure while also lowering the capacitance for thenanostructure device.

In an embodiment, a method includes forming a first multi-layer stackover a semiconductor substrate, the first multi-layer stack including afirst sacrificial layer over a semiconductor substrate, a first channellayer over the first sacrificial layer, a second sacrificial layer overthe first channel layer, and a second channel layer over the secondsacrificial layer, the first sacrificial layer having a first atomicconcentration of a first semiconductor element, the second sacrificiallayer having a second atomic concentration of the first semiconductorelement, the second atomic concentration being less than the firstatomic concentration. The method also includes patterning themulti-layer stack and the semiconductor substrate to form a firsttrench. The method also includes forming an isolation region in thefirst trench. The method also includes forming a first gate stack overthe patterned multi-layer stack and isolation region. The method alsoincludes etching the patterned multi-layer stack to form a first recessadjacent the first gate stack, the etching including an isotropicetching process. The method also includes epitaxially growing a firstsource/drain region in the first recess. The method also includesreplacing the first gate stack and the first and second sacrificiallayers of the patterned and etched multi-layer stack with a second gatestack, the second gate stack surrounding the etched first channel layerand the etched second channel layer.

Embodiments may include one or more of the following features. Themethod where the first semiconductor element is germanium. The firstsacrificial layer includes silicon germanium. Etching the patternedmulti-layer stack to form the first recess etches the first sacrificiallayer at a first etch rate and etches the second sacrificial layer at asecond etch rate, the second etch rate being less than the first etchrate. The first sacrificial layer has the first atomic concentration ofthe first semiconductor element throughout the entirety of the firstsacrificial layer. Forming the first multi-layer stack over thesemiconductor substrate further includes epitaxially growing each of thefirst sacrificial layer, the first channel layer, the second sacrificiallayer, and the second channel layer. Etching the patterned multi-layerstack to form the first recess adjacent the first gate stack furtherincludes anisotropically etching the patterned multi-layer stack and thesemiconductor substrate, and after anisotropically etching,isotropically etching the patterned multi-layer stack and thesemiconductor substrate, the isotropically etching step recessingsidewalls of the first and second sacrificial layers of the patternedmulti-layer stack. After the second gate stack is formed, the innerspacer is between the second gate stack and the first source/drainregion. The inner spacer includes multiple spacer layers havingdifferent material compositions.

In an embodiment, a method includes forming a first multi-layer finstructure over a semiconductor substrate, forming the first multi-layerfin structure including epitaxially growing a first sacrificial layerover a semiconductor substrate, the first sacrificial layer having afirst portion and a second portion, the first portion having a firstatomic concentration of a first semiconductor element, the secondportion having a second atomic concentration of the first semiconductorelement, the second atomic concentration being different than the firstatomic concentration. The method also includes epitaxially growing afirst channel layer from the first sacrificial layer. The method alsoincludes epitaxially growing a second sacrificial layer from the firstchannel layer, the second sacrificial layer having a first portion and asecond portion, the first portion having a third atomic concentration ofthe first semiconductor element, the second portion having a fourthatomic concentration of the first semiconductor element, the fourthatomic concentration being different than the third atomicconcentration. The method also includes epitaxially growing a secondchannel layer from the second sacrificial layer. The method alsoincludes and patterning the multi-layer first sacrificial layer, thefirst channel layer, the second sacrificial layer, the second channellayer, and the semiconductor substrate to form the multi-layer finstructure. The method also includes forming a dummy gate stack over themulti-layer fin structure. The method also includes etching themulti-layer fin structure to form a first recess adjacent the dummy gatestack, the etching including an isotropic etching process. The methodalso includes epitaxially growing a first source/drain region in thefirst recess. The method also includes replacing the dummy gate stackand the first and second sacrificial layers of the etched multi-layerfin structure with an active gate stack, the active gate stacksurrounding the etched first channel layer and the etched second channellayer.

Embodiments may include one or more of the following features. Themethod where after etching the multi-layer fin structure, the etchedfirst and second sacrificial layers of the etched multi-layer finstructure have planar sidewalls. After etching the multi-layer finstructure, the etched first and second sacrificial layers of the etchedmulti-layer fin structure have notched sidewalls. After etching themulti-layer fin structure, the etched first and second sacrificiallayers of the etched multi-layer fin structure have tapered sidewalls.The first semiconductor element is germanium. The first portion of thefirst sacrificial layer is a top portion of the first sacrificial layer,the second portion of the first sacrificial layer being a middle portionof the first sacrificial layer, the top portion and a bottom portion ofthe first sacrificial layer having a higher atomic concentration of thefirst semiconductor element than the middle portion of the firstsacrificial layer, the middle portion being between the top and bottomportions.

In an embodiment, a semiconductor device includes a first channel regionover a semiconductor substrate. The semiconductor device also includes asecond channel region over the first channel region. The semiconductordevice also includes a first gate stack over the semiconductor substrateand surrounding the first channel region and the second channel region.The semiconductor device also includes a first inner spacer extendingfrom the first channel region to the second channel region and along asidewall of the first gate stack. The semiconductor device also includesa second inner spacer extending from the first channel region to thesecond channel region and along a sidewall of the first inner spacer,the second inner spacer having a different material composition than thefirst inner spacer. The semiconductor device also includes a firstsource/drain region adjacent the first channel region, the secondchannel region, and the second inner spacer, the first and second innerspacers being between the first gate stack and the first source/drainregion.

Embodiments may include one or more of the following features. Thesemiconductor device where the first inner spacer physically contactsthe first gate stack, and where the second inner spacer physicallycontacts the first source/drain region. The first inner spacerphysically contacts the first gate stack at a concave surface of thefirst gate stack. The first inner spacer includes SiCN, and where thesecond inner spacer includes SiN. The first inner spacer and the secondinner spacer each extend from a top surface of the first channel regionto a bottom surface of the second channel region.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method comprising: forming a multi-layer stackover a semiconductor substrate, the multi-layer stack comprising a firstsacrificial layer over a semiconductor substrate, a first channel layerover the first sacrificial layer, a second sacrificial layer over thefirst channel layer, and a second channel layer over the secondsacrificial layer, the first sacrificial layer having a first atomicconcentration of a first semiconductor element, the second sacrificiallayer having a second atomic concentration of the first semiconductorelement, the second atomic concentration being less than the firstatomic concentration; patterning the multi-layer stack and thesemiconductor substrate to form a first trench; forming an isolationregion in the first trench; forming a first gate stack over thepatterned multi-layer stack and isolation region; etching the patternedmulti-layer stack to form a first recess adjacent the first gate stack,the etching comprising an isotropic etching process; epitaxially growinga first source/drain region in the first recess; and replacing the firstgate stack and the first and second sacrificial layers of the patternedand etched multi-layer stack with a second gate stack, the second gatestack surrounding each of the etched first channel layer and the etchedsecond channel layer.
 2. The method of claim 1, wherein the firstsemiconductor element is germanium.
 3. The method of claim 2, whereinthe first sacrificial layer comprises silicon germanium.
 4. The methodof claim 1, wherein etching the patterned multi-layer stack to form thefirst recess etches the first sacrificial layer at a first etch rate andetches the second sacrificial layer at a second etch rate, the secondetch rate being less than the first etch rate.
 5. The method of claim 1,wherein the first sacrificial layer has the first atomic concentrationof the first semiconductor element throughout the entirety of the firstsacrificial layer.
 6. The method of claim 1, wherein forming the firstmulti-layer stack over the semiconductor substrate further comprisesepitaxially growing each of the first sacrificial layer, the firstchannel layer, the second sacrificial layer, and the second channellayer.
 7. The method of claim 1, wherein etching the patternedmulti-layer stack to form the first recess adjacent the first gate stackfurther comprises: anisotropically etching the patterned multi-layerstack and the semiconductor substrate; and after anisotropicallyetching, isotropically etching the patterned multi-layer stack and thesemiconductor substrate, the isotropically etching step recessingsidewalls of the first and second sacrificial layers of the patternedmulti-layer stack.
 8. The method of claim 7 further comprising: formingan inner spacer on the recessed sidewalls of the first and secondsacrificial layers, wherein after the second gate stack is formed, theinner spacer is between the second gate stack and the first source/drainregion.
 9. The method of claim 8, wherein the inner spacer comprisesmultiple spacer layers having different material compositions.
 10. Amethod comprising: forming a multi-layer fin structure over asemiconductor substrate, forming the multi-layer fin structurecomprising: epitaxially growing a first sacrificial layer over asemiconductor substrate, the first sacrificial layer having a firstportion and a second portion, the first portion having a first atomicconcentration of a first semiconductor element, the second portionhaving a second atomic concentration of the first semiconductor element,the second atomic concentration being different than the first atomicconcentration; epitaxially growing a first channel layer from the firstsacrificial layer; epitaxially growing a second sacrificial layer fromthe first channel layer, the second sacrificial layer having a firstportion and a second portion, the first portion having a third atomicconcentration of the first semiconductor element, the second portionhaving a fourth atomic concentration of the first semiconductor element,the fourth atomic concentration being different than the third atomicconcentration; epitaxially growing a second channel layer from thesecond sacrificial layer; and patterning the first sacrificial layer,the first channel layer, the second sacrificial layer, the secondchannel layer, and the semiconductor substrate to form the multi-layerfin structure; forming a dummy gate stack over the multi-layer finstructure; etching the multi-layer fin structure to form a first recessadjacent the dummy gate stack, the etching comprising an isotropicetching process; epitaxially growing a first source/drain region in thefirst recess; and replacing the dummy gate stack and the first andsecond sacrificial layers of the etched multi-layer fin structure withan active gate stack, the active gate stack surrounding the etched firstchannel layer and the etched second channel layer.
 11. The method ofclaim 10, wherein after etching the multi-layer fin structure, theetched first and second sacrificial layers of the etched multi-layer finstructure have planar sidewalls.
 12. The method of claim 10, whereinafter etching the multi-layer fin structure, the etched first and secondsacrificial layers of the etched multi-layer fin structure have notchedsidewalls.
 13. The method of claim 10, wherein after etching themulti-layer fin structure, the etched first and second sacrificiallayers of the etched multi-layer fin structure have tapered sidewalls.14. The method of claim 10, wherein the first semiconductor element isgermanium.
 15. The method of claim 10, wherein the first portion of thefirst sacrificial layer is a top portion of the first sacrificial layer,the second portion of the first sacrificial layer being a middle portionof the first sacrificial layer, the top portion and a bottom portion ofthe first sacrificial layer having a higher atomic concentration of thefirst semiconductor element than the middle portion of the firstsacrificial layer, the middle portion being between the top and bottomportions.
 16. A method comprising: forming a first sacrificial layerover a semiconductor substrate; forming a first channel region over thefirst sacrificial layer, the first sacrificial layer having a firstatomic concentration of a first semiconductor element; forming a secondsacrificial layer over the first channel region; forming a secondchannel region over the second sacrificial layer, the second sacrificiallayer having a second atomic concentration of the first semiconductorelement, the second atomic concentration being less than the firstatomic concentration; forming a first gate stack over the semiconductorsubstrate, the first channel region, the first sacrificial layer, thesecond sacrificial layer, and the second channel region; forming a firstinner spacer extending from the first channel region to the secondchannel region and along a sidewall of the first gate stack; forming asecond inner spacer extending from the first channel region to thesecond channel region and along a sidewall of the first inner spacer,the second inner spacer having a different material composition than thefirst inner spacer, the first inner spacer and the second inner spacereach physically contacting a top surface of the first channel region anda bottom surface of the second channel region; epitaxially growing afirst source/drain region adjacent the first channel region, the secondchannel region, and the second inner spacer, the first source/drainregion physically contacting the first channel region; and replacing thefirst gate stack and the first and second sacrificial layers with asecond gate stack, the second gate stack surrounding each of the firstchannel region and the second channel region, the first and second innerspacers being between the second gate stack and the first source/drainregion.
 17. The method of claim 16, wherein the first inner spacerphysically contacts the second gate stack, and wherein the second innerspacer physically contacts the first source/drain region.
 18. The methodof claim 17, wherein the first inner spacer physically contacts thesecond gate stack at a concave surface of the second gate stack.
 19. Themethod of claim 16, wherein the first inner spacer comprises SiCN, andwherein the second inner spacer comprises SiN.
 20. The method of claim16, wherein the first inner spacer and the second inner spacer eachextend from a top surface of the first channel region to a bottomsurface of the second channel region.